1 / 37

RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology. RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY. L 7: X Ray beam. Introduction. A review is made of:

aran
Download Presentation

RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION INDIAGNOSTIC ANDINTERVENTIONAL RADIOLOGY L 7: X Ray beam

  2. Introduction • A review is made of: • The production of X Rays for diagnostic radiology : Bremsstrahlung and characteristic X Rays • Beam filtration,scattering of X Rays, Quality and quantity of X Rays, X Ray spectrum and factors affecting X Ray spectrum 7: X Ray beam

  3. Topics • Bremsstrahlung production • Characteristic X Rays • Beam filtration • Scattered radiation • Factors affecting X Ray spectrum, Quantity and Quality 7: X Ray beam

  4. Overview • To become familiar with the technological principles of the X Ray production. 7: X Ray beam

  5. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 7: X Ray beam Topic 1: Bremsstrahlung production

  6. Electron-nucleus interaction (I) • Bremsstrahlung: • radiative energy loss (E) by electrons slowing down on passage through a material •  is the deceleration of the incident electron by the nuclear Coulomb field •  radiation energy (E) (photon) is emitted. 7: X Ray beam

  7. Electron-nucleus interaction (II) • With materials of high atomic number • the energy loss is higher • The energy loss by Bremsstrahlung • > 99% of kinetic E loss as heat production • it increases with increasing electron energy • X Rays are dominantly produced by Bremsstrahlung 7: X Ray beam

  8. Electrons strike the nucleus N N Bremsstrahlung spectrum E E n(E) n1E1 n2E2 n1 n3E3 n2 n3 Emax E1 E1 E2 E2 E3 E3 7: X Ray beam

  9. Bremsstrahlung continuous spectrum • Energy (E) of Bremsstrahlung photons may take any value between “zero” and the maximum kinetic energy of incident electrons • Number of photons as a function of E is proportional to 1/E • Thick target  continuous linear spectrum 7: X Ray beam

  10. Bremsstrahlung spectra dN/dE dN/dE (spectral density) E0 E0 E E From a “thick” target From a “thin” target E = energy of emitted photons E0= energy of electrons 7: X Ray beam

  11. X Ray spectrum energy (continuous part) • Maximum energy of Bremsstrahlung photons • kinetic energy of incident electrons • In X Ray spectrum of radiology installations: • Max (energy) = X Ray tube peak voltage E Bremsstrahlung Bremsstrahlung after filtration keV keV 50 100 150 200 7: X Ray beam

  12. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 7: X Ray beam Topic 2: Characteristic X Rays

  13. Characteristic X Rays: Electron-Electron interaction (I) • Starts with ejection of e- mainly from k shell (also possible for L, M,…) by ionization • e- from L or M shell fall into the vacancy created in the k shell • Energy difference is emitted as photons • A sequence of successive electron transitions between energy levels • Energy of emitted photons is characteristic of the atom 7: X Ray beam

  14. Characteristic X Rays (II) Energy (eV) K1 100 80 60 40 20 - 20 - 70 - 590 - 2800 - 11000 - 69510 K2 6 5 4 3 2 0 P K1 O N L L K2 M L L 0 10 20 30 40 50 60 70 80 (keV) K 7: X Ray beam

  15. Atom characteristics • A, Z and associated quantities • Hydrogen A = 1 Z = 1 EK= 13.6 eV • Carbon A = 12 Z = 6 EK= 283 eV • Molybdenum A = 96 Z = 42 EK= 19.0 keV • Tungsten A = 183 Z = 74 EK= 69.5 keV • Uranium A = 238 Z = 92 EK= 115.6 keV 7: X Ray beam

  16. Radiation emitted by the X Ray tube • Primary radiation: before interacting photons • Scattered radiation: after at least one interaction; need for Antiscatter grid • Leakage radiation: not absorbed by the X Ray tube housing shielding • Transmitted radiation: emerging after passage through matter 7: X Ray beam

  17. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 7: X Ray beam Topic 3: X Ray Beam filtration

  18. What is beam filtration? Absorber placed between Source and object Will preferably absorb the lower energy photons Or absorb parts of spectrum (K-edge filters) X Ray spectrum at 30 kV for an X Ray tube with a Mo target and a 0.03 mm Mo filter 15 10 5 Number of photons (arbitrary normalisation) 10 15 20 25 30 Energy (keV) 7: X Ray beam

  19. Tube filtration • Inherent filtration (always present) • reduced entrance (skin) dose to the patient (cut off the low energy X Rays which do not contribute to the image) • Additional filtration (removable filter) • further reduction of patient skin and superficial tissue dose without loss of image quality • Total filtration (inherent + added) • Total filtration must be > 2.5 mm Al for a > 110 kV generator • Measurement of filtration  Half-Value Layer 7: X Ray beam

  20. Tube filtration Exit window Filter 7: X Ray beam

  21. Filtration Change in QUANTITY & Change in QUALITY spectrum shifts to higher energy 1- Spectrum out of anode 2- After window tube housing (INHERENT filtration) 3- After ADDITIONAL filtration 7: X Ray beam

  22. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 7: X Ray beam Topic 4: Scattered radiation

  23. Radiation emitted by the X Ray tube • Primary radiation : before interacting photons • Scattered radiation : after at least one interaction • Leakage radiation : not absorbed by the X Ray tube housing shielding • Transmitted radiation : emerging after passage through matter Antiscatter grid 7: X Ray beam

  24. Scattered radiation • Effect on image quality • loss of contrast • Effect on patient dose • increasing of superficial and depth dose • Possible reduction through : •  use of grid •  limitation of the field to the useful portion •  limitation of the irradiated volume (e.g.:breast compression in mammography) 7: X Ray beam

  25. Anti scatter grid (I) • Radiation emerging from the patient • primary beam: contributes to the image • scattered radiation: reduces image contrast and contributes to the major part of the patient dose • the grid (between patient and film) eliminates most of scattered radiation • stationary grid • moving grid (better performance) • focused grid • Potter-Bucky system 7: X Ray beam

  26. Anti scatter grid (II) Source of -rays Patient Scattered X Rays Lead Film and cassette Useful X Rays 7: X Ray beam

  27. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 7: X Ray beam Topic 5: Factors affecting X Ray spectrum

  28. FACTORS AFFECTING X Ray BEAM • TUBE CURRENT • TUBE POTENTIAL • FILTRATION • HIGH OR LOW Z TARGET MATERIAL • TYPE OF WAVEFORM 7: X Ray beam

  29. X Ray spectrum: tube current 400 mA Number of X Rays per unit Energy 200 mA X Ray Energy (keV) 7: X Ray beam

  30. X Ray spectrum: tube current Change of QUANTITY NO change of quality Effective kV not changed 7: X Ray beam

  31. X Ray spectrum: tube potential Change in QUANTITY & Change in QUALITY - spectrum shifts to higher Energy - characteristic lines appear 7: X Ray beam

  32. X Ray spectrum: filtration Change in QUANTITY & Change in QUALITY spectrum shifts to higher energy 1- Spectrum out of anode 2- After window tube housing (INHERENT filtration) 3- After ADDITIONAL filtration 7: X Ray beam

  33. X Ray spectrum: Target Z Higher Z Number of X Rays per unit Energy Lower Z X Ray Energy (keV) 7: X Ray beam

  34. X Ray spectrum: Target Z Three Phase Number of X Rays per unit Energy Single Phase X Ray Energy (keV) 7: X Ray beam

  35. X Ray Quantity TUBE CURRENT (mA) EXPOSURE TIME (s) TUBE POTENTIAL (kVp) WAVEFORM DISTANCE (FSD) FILTRATION X Ray Quality TUBE POTENTIAL (kVp) FILTRATION WAVE FORM Factors affecting 7: X Ray beam

  36. Summary • We learned about the continuous Bremsstrahlung spectrum and the characteristic lines • Several factors (kV,filtration,current, waveform,target material) influence quality and/or quantity of the X Ray beam 7: X Ray beam

  37. Where to Get More Information • The Essential Physics of Medical Imaging. JT Bushberg, JA Seibert, EM Leidholdt, JM Boone. Lippincott Williams & Wilkins, Philadelphia, 2011 7: X Ray beam

More Related